This invention relates to a variable-camber airfoil, and more particularly to a mechanism for varying the camber of the forward section of the airfoil.
Common structures used to modify the lift characteristics of an airfoil, especially for low-speed operation, are auxiliary leading edge devices, commonly referred to as flaps that pivot, or slats that slide outwardly from the leading edge of the airfoil into a deployed position. When deployed, such devices normally increase the effective wing area and camber of the wing to improve the overall lift characteristics during low speed flight. A drawback with such devices is that they are not able to be deployed to intermediate positions and still maintain the proper flow of air over the airfoil. In particular, during and after deployment, there is an interruption of smooth airflow over the critical airfoil upper surface resulting in an increase in drag and an undesirable lift modification.
To overcome this shortcoming of these leading edge devices used to aid the lift of an airfoil, various prior art devices have appeared that vary the camber of the airfoil by bending the aerodynamic skin surfaces, and thus modify the lift characteristics of the airfoil. Such prior art variable-camber airfoils generally act by changing the shape of flexible upper and/or lower skins to vary the camber of the airfoil surface. One drawback of prior art variable-camber airfoils has been their ability to efficiently satisfy only one or two flight modes, e.g., takeoff and/or landing. If a variable-camber airfoil is to be used on an aircraft, it is desirable to be able to adjust the airfoil contour so that it is usable in a variety of flight modes besides those for takeoff and landing, e.g., during cruise and climb modes, as well as being usable as a trim device to lower aerodynamic drag experienced by the airfoil.
Another drawback of prior art variable-camber airfoils has been the aerodynamic drag induced by multiple discontinuities or breaks present in the lower surface of the airfoils. These breaks occur where airfoil sections abut or overlap one another when the camber of the airfoil is altered, generally from a position other than that employed in the cruise mode. It would, of course, be desirable to decrease or eliminate the aerodynamic drag caused by multiple breaks on the airfoil lower surface during flight conditions in order to increase the flight performance and efficiency of the airfoil.
Furthermore, it is generally desirable for an airfoil camber altering mechanism to be as light in weight as possible while maintaining the requisite stiffness required to efficiently alter the camber of the airfoil, thereby minimizing any weight penalty imposed on an aircraft using a variable-camber airfoil. Additionally, it is desirable for a camber altering mechanism to be relatively simple mechanically in order to decrease maintenance and manufacturing costs while maintaining a high degree of reliability.